Emit a hint when using generic method comment syntax (issue 30356)

pkg/analyzer/lib/src/dart/error/hint_codes.dart

Index: pkg/analyzer/lib/src/dart/error/hint_codes.dart
diff --git a/pkg/analyzer/lib/src/dart/error/hint_codes.dart b/pkg/analyzer/lib/src/dart/error/hint_codes.dart
index c71dd30cdd2c2c47010d074050b6c32615183a67..48de43d59a0a561da7b876a695dd451e504d1d57 100644
--- a/pkg/analyzer/lib/src/dart/error/hint_codes.dart
+++ b/pkg/analyzer/lib/src/dart/error/hint_codes.dart
@@ -162,6 +162,15 @@ class HintCode extends ErrorCode {
           "Try using a package: URI instead.");
 
   /**
+   * Generic type comments (`/*<T>*/` and `/*=T*/`) are no longer necessary and
+   * will soon be ignored.
+   */
+  static const HintCode GENERIC_METHOD_COMMENT = const HintCode(
+      'GENERIC_METHOD_COMMENT',
+      "The generic type comment is being deprecated in favor of the real syntax.",
+      "Try replacing the comment with the actual type annotation.");
+
+  /**
    * Deferred libraries shouldn't define a top level function 'loadLibrary'.
    */
   static const HintCode IMPORT_DEFERRED_LIBRARY_WITH_LOAD_FUNCTION =